Tapered rotor-stator air gap for superconducting synchronous machine

Abstract

A synchronous machine is disclosed comprising a rotor coupled to a rotor cooling system; a stator around the rotor and separated from the rotor by an annular gap between the rotor and an inner surface of the stator, wherein the annular gap has a variable thickness along a length of the gap, and a stator ventilation system independent of the rotor cooling system, wherein the stator ventilation system forces cooling gases through the annular gap.

What is claimed is:  
     
       1. A synchronous machine comprising: 
       a rotor coupled to a rotor cooling system;  
       an annular stator around the rotor and having radial cooling passages;  
       an annular gap between the rotor and the stator, and said annular gap has a variable thickness along a length of the gap, and  
       a stator ventilation system providing cooling gases through said annular gap and said cooling passages in the stator.  
     
     
       2. A synchronous machine as in  claim 1  wherein said thickness of the annular gap is thickest at a center portion of the length of the gap. 
     
     
       3. A synchronous machine as in  claim 1  wherein said thickness of the annular gap is thicker at a center portion of the length of the gap than at an end portion of said annular gap. 
     
     
       4. A synchronous machine as in  claim 1  wherein said thickness of the annular gap increases non-linearly from an end portion of the gap towards a center portion of the gap. 
     
     
       5. A synchronous machine as in  claim 1  wherein said thickness of the annular gap increases non-linearly along the length of the gap. 
     
     
       6. A synchronous machine as in  claim 1  wherein said annular gap has an inner cylindrical surface formed by a shield on a rotor core section of the rotor, and said shield has a variable thickness. 
     
     
       7. A synchronous machine as in  claim 1  wherein said annular gap has an inner cylindrical surface defined by a shield on a rotor core of the rotor, and said shield has a tapered outer surface adjacent the inner cylindrical surface of the gap. 
     
     
       8. A synchronous machine as in  claim 1  wherein said annular gap has a tapered inner cylindrical surface defined by the rotor. 
     
     
       9. A synchronous machine as in  claim 1  wherein said rotor comprises a superconducting coil, and said rotor cooling system provides cryogenic cooling fluid to said coil. 
     
     
       10. A synchronous machine as in  claim 1  which is an electromagnetic generator. 
     
     
       11. A synchronous machine as in  claim 1  which is a motor. 
     
     
       12. A synchronous machine as in  claim 1  wherein said ventilation system is a reverse flow ventilation system. 
     
     
       13. A synchronous machine as in  claim 1  wherein said ventilation system is a closed-loop system in which cooling gas circulates through the gap, stator and a heat exchanger. 
     
     
       14. A synchronous machine as in  claim 1  wherein variable thickness of the annular gap is non-linear along the length of the gap and is provided by a segmented steps on an outer cylindrical surface of the rotor. 
     
     
       15. A superconducting electromagnetic machine comprising: 
       a solid core rotor having a cryogenically cooled superconducting rotor coil winding;  
       a stator coaxial with said rotor and having stator coils magnetically coupled with said superconducting rotor coil winding, said stator coils arranged around said rotor, and said stator having cooling passages extending outwardly from an inner periphery of the stator, said inner periphery separated from the rotor by an annular rotor gap, wherein said rotor having a cylindrical surface tapered non-linearly along an axis of the stator and said rotor gap has a tapered thickness along a length of the gap;  
       said rotor being cooled by a cryogenic cooling fluid, and  
       a stator ventilation system providing cooling gas to said annular rotor gap and said passages of the stator.  
     
     
       16. A synchronous machine as in  claim 15  wherein said annular gap is thickest at a center portion of the length of the gap. 
     
     
       17. A synchronous machine as in  claim 15  wherein said annular gap is thicker at a center portion of the length of the gap than at an end portion of said annular gap. 
     
     
       18. A synchronous machine as in  claim 15  wherein said thickness of the annular gap gradually increases from an end portion of the gap towards a center portion of the gap. 
     
     
       19. A synchronous machine as in  claim 15  wherein said annular gap has a sloped inner cylindrical surface defined by a shield on a rotor core section of the rotor. 
     
     
       20. A synchronous machine as in  claim 19  wherein said shield a tapered surface forming the inner cylindrical surface of the gap. 
     
     
       21. A synchronous machine as in  claim 15  wherein said annular gap has a sloped outer cylindrical surface defined by the stator. 
     
     
       22. A machine as in  claim 15  wherein the surface of the rotor is segmented in steps to form the tapered thickness of the gap. 
     
     
       23. A method for cooling a superconducting electromagnetic machine having a rotor core including a superconducting rotor coil winding and a stator core and a stator ventilation system, said method comprising the steps of: 
       a. cryogenically cooling the rotor coil winding;  
       b. moving cooling gas into an annular gap between the rotor and stator, wherein said annular gap is tapered along a length of the gap, and  
       c. the cooling gas flowing from the gap into ducts of the stator, wherein said ducts have openings adjacent the gap and along a length of the gap.  
     
     
       24. A method for cooling as in  claim 23  wherein the annular gap is thickest at a center portion along the length of the gap, and said gap increases in thickness non-linearly along the length of the gap. 
     
     
       25. A method for shaping a gap between a rotor and a stator in a synchronous electromagnetic machine, said method comprising the steps of: 
       a. forming the stator having a cylindrical cavity to receive said rotor, wherein said stator includes cooling ducts open to said cavity;  
       b. forming a cylindrical rotor surface on said rotor, wherein said rotor surface forms an inner cylindrical surface of said gap, and  
       c. shaping the rotor surface to taper a thickness of the gap along a length of the gap.  
     
     
       26. A method for shaping a gap between a rotor and a stator as in  claim 25  further comprising selecting said non-linear taper of the gap to uniformly distribute cooling gas into the cooling ducts of the stator core. 
     
     
       27. A method for shaping a gap between a rotor and a stator as in  claim 25  further comprising thickening the gap at a center portion of the gap.